This invention relates to the detection and processing of rapidly changing bioelectric or other signals. More particularly, it relates to methods for detecting, processing smoothing signals having rapidly changing amplitudes, such as EMG signals, which may be generated by the tongue or other muscles, and for providing stable and discrete output signals from input signals detected by a detector, such as an intraoral device.
The use of electromyographic (EMG) signals for control of a prosthesis was proposed by Reiter in 1948. In 1958, an actual surface EMG or myoelectrically controlled prosthetic hand was introduced in Russia. EMG signals recorded from remaining agonist and antagonist muscles in the residual limb of a transradial amputee were used. Since the 1960""s, the use of myoelectric control of prostheses and orthoses has continued to be studied and successfully implemented. There are now myoelectric prosthetic devices which use surface EMG signals recorded from one or two muscle sites for proportional or digital actuation of one or more functions of an electric powered prosthetic component.
During the late 1960""s and early 1970""s, electromyographic or myoelectric based control strategies were studied and compared with myomechanical position controllers. The use of surface EMG or myoelectric controllers has been limited by the long integration intervals required to stabilize rapidly fluctuating surface EMG signals. These long integration intervals slow down the responsivity of the controller. A second limitation of myoelectric controllers has been the small number of resolvable discrete control signal levels obtainable (approximately five). Myomechanical position controlling systems have been found to provide a greater number of discrete control levels, as well as more stable control signals.
A myomechanical technique has been developed for use with mid-cervical spinal cord injured individuals using shoulder movement transduction for proportional two-axis control of prosthetic and orthotic systems, including systems employing functional electrical stimulation. Limitations in using shoulder movement transduction for proportional two-axis control of orthotic and neuroprosthetic systems in the high quadriplegic include a) a decrease in the number of discrete control signal levels achievable and a decrease in the stability of the control signals as the level of spinal cord injury become higher, b) control signal interference from motion of the contralateral shoulder, c) instability of reference position due to postural changes and attachment methods of the position transduce, and d) difficulty in concealing the transducer. Recently there has been renewed interest in using processed surface EMG or myoelectric signals as control signals in spinal cord injured individuals in a single dimensional functional electrical stimulation task.
Oral motor and sensory impairments, including dysphagia and dysarthria, can result from many causes including: traumatic brain injury, cerebral palsy, stroke and other diseases of the nervous system such as Parkinson""s disease, multiple sclerosis and amyotrophic lateral sclerosis. The occurrence of oral motor and sensory dysfunction increases with age and can result in increased difficulty with communication, decline in nutritional status and, in some cases, aspiration pneumonia. Improved methods for measuring intraoral motor and sensory function are needed.
Electromyographic (EMG) signals from the genioglossus muscle have been previously measured using surface electrodes placed over the skin under the mandible and using surface electrodes mounted to mandibular appliances or splints. With previous intraoral EMG recording techniques, two to four electrodes are used. Electrode wires exit the mouth anteriorly between the upper and lower incisors and hinder approximation of the teeth.
The mounting of two surface electrodes 3 mm in diameter to the palate side of a maxillary splint has been described by Schwarts, et al. Used to stimulate the soft palate, these electrodes were located 1 cm apart, centered to midline, and 2-3 cm posterior to the vibrating line on the soft palate. The methods by which the two electrode wires exited the mouth was not described.
U.S. Pat. No. 5,212,476 invented by Sean R. Maloney describes an intraoral device for detecting EMG signals from the tongue. The Maloney device describes a single splint having a convex side which may be in contact with either the maxillary or mandibular and includes active electrodes mounted on the splint adjacent to the tongue.
It is therefore one object of the invention to provide an improved method for smoothing input signals having rapidly changing amplitudes.
It is another object of the invention to provide an improved method for converting EMG signals generated from the tongue to signals having stable and discrete levels.
It is still another object of the invention to provide an improved intraoral device for detecting EMG signals from the tongue.
One aspect of this invention calls for digital processing techniques which can smooth and stabilize a bioelectric of other signal amplitude and an integrated (with respect to time) bioelectric or other integrated signal amplitude which change rapidly in an irregular or random (stochastic) fashion due to the asynchronous nature of the constituent or contributing components of the signal or integrated signal amplitude. The fluctuatory signal amplitude to be processed can be a unipolar (+ or xe2x88x92) or a bipolar (+ and xe2x88x92) signal amplitude. Examples of bipolar bioelectric signal amplitudes which can be processed using the techniques include electromyographic (EMG) or myoelectric, electroneurographic (ENG) or nerve, and electroencephalographic (EEG) or brain signal amplitudes.
These signal processing techniques decrease signal or integrated signal amplitude variability (i.e., smooth the signal or integrated signal amplitude) using an adaptive moving average process and an exponential average process while maintaining signal or integrated signal amplitude responsiveness (i.e., adequate rate of signal or integrated signal amplitude change for a given application). The signal or integrated signal amplitude is stabilized by converting the smoothed but still fluctuating signal or integrated signal amplitude into a discrete signal, or integrated signal, amplitude using an interactive variable windowing process. Smoothing the varying signal or integrated signal amplitude prior to forming a discrete or stable signal or integrated signal amplitude increases the number of resolvable signal or integrated signal amplitude values. Using this signal or integrated signal amplitude stabilizing technique allows the discrete signal or integrated signal value to be maintained for a time interval suitable for the digital signal processing application.
One potential application for these digital signal processing techniques is the conversion of a fluctuating surface electromyographic (EMG) signal amplitude or integrated surface EMG signal amplitude into a processed myoelectric, signal or integrated signal, amplitude to control orthotic (brace), prosthetic (artificial limb), neuroprosthetic (prosthesis which uses limb functional electrical stimulation), robotics, and other (external) devices.
A second application for these digital signal processing techniques is the conversion of a bioelectric or other randomly changing signal, or integrated signal, amplitude into a series of discrete signal amplitudes or discrete integrated signal amplitudes for signal or integrated signal amplitude measurement purposes. These techniques allow resolution of the processed signal amplitude or integrated signal amplitude into discrete time and discrete signal amplitude or integrated signal amplitude domains. For example, rectified EMG or integrated EMG signal amplitudes could be processed into smoothed and stabilized discrete amplitude or integrated amplitude values. These discrete values could then be plotted as a function of time or sorted by discrete signal value for a given length of time and plotted as a histogram.
In accordance with one form of the invention, there is provided a method for smoothing input signals having rapidly changing amplitudes utilizing an adaptive moving average processor. The method includes the steps of: providing a plurality of parallel moving average processes; each of the moving average processes for averaging a different number of signals; each of the processes receive the input signals; providing a differentiator which receives an average of the signals from one of the processes for determining the rate of change of the signals; and selecting one of the processes for providing an output of the average of the signals based on the rate of change of the signal. The words xe2x80x9cmoving average processxe2x80x9d are used to describe a portion of a computer program which calculates the moving average of the signal or integrated signal amplitudes over a period of time.
In accordance with another form of the invention, there is provided a method for smoothing input signals having rapidly changing amplitudes utilizing a compound moving average processor. The method includes the steps of: providing at least first and second moving average processes in series; providing a rapidly changing input signal to the first process; the averaged output signal from the first process becoming the input signal to the second process, so that the responsiveness of the first and second processors is greater than the responsiveness of a single moving average process which calculates the average of the same number of signal amplitudes as the combination of the first and second processes.
In accordance with another form of the invention, there is provided a method for smoothing input signals having rapidly changing amplitudes utilizing an adaptive moving average processor. The method includes the steps of: calculating the moving average of input signal amplitudes for a first predetermined period of time; calculating the moving average of input signals for a second predetermined period of time which includes the first period of time, whereby more signals are averaged during the second predetermined period of time than the first predetermined period of time; determining the rate of change of the amplitudes of the signals; selecting only one of the calculated averages based on the rate of change of the signal amplitudes; and selecting the second calculated average if the rate of change of the signal amplitude is low.
In accordance with another form of the invention, there is provided a method for smoothing input signals having rapidly changing amplitudes utilizing a compound moving average processor. The method includes the steps of: calculating the moving average value of the amplitude of the input signals, thereby providing a first average of the input signal amplitudes; and calculating the moving average value of the output of the first calculation of moving average, whereby the responsiveness for the first calculation and the second calculation is greater than the responsiveness of a single calculation which calculates the average of the same number of signal amplitudes as the first and second calculations.
In accordance with another form of the invention, there is provided a method for converting EMG signals having rapidly changing amplitudes to signals having stable and discrete levels. The method includes the steps of: detecting EMG signals from electrodes on an intraoral device; amplifying the EMG signals; converting the EMG signals to digital format; providing a moving average of the amplitudes of the EMG signals; and windowing the average signals to discrete and stable amplitude levels.
In accordance with another form of the invention, there is provided an intraoral device for detecting EMG signals from the tongue. The device includes a maxillary splint and a mandibular splint. The maxillary splint has a palate side which is adapted to be in contact with the palate of a patient. The mandibular splint has a gum side which is adapted to be in contact with the gum of the patient. At least one reference electrode is attached to the palate side of the maxillary splint. At least one active electrode is attached to the gum side of the mandibular splint. The reference electrode will make contact with the patient""s palate and the active electrode will make contact with the patient""s gum so that the detection of EMG signals from the tongue is enhanced.
In accordance with another form of the invention, there is provided an intraoral device for detecting EMG signals from the tongue. The device includes a splint having at least one electrode attached thereto. The splint is made of acrylic. Woven fiberglass is imbedded in the acrylic for increasing the strength of the splint. The woven fiberglass may be twisted near its midpoint.